As illustrated in FIG. 9, a scroll compressor includes a fixed scroll 10 having an end plate and a spiral wall 10c extending upright from the end plate, an orbiting scroll 11 arranged so as to oppose the fixed scroll 10 and having an end plate and a spiral wall 11c extending upright from the end plate, the spiral walls 10c, 11c of a pair of the scrolls are engaged with each other, and the orbiting scroll 11 is orbited (is caused to make an orbital motion) by a revolving shaft having an eccentric shaft in a state of being restricted from rotating, so that a compression chamber 15 formed between the spiral walls of both of the scrolls is moved toward the center while a volume thereof being reduced to compress a working fluid.
Each of the spiral walls 10c, 11c is formed so as to draw an involute curve, and the compression chamber 15 includes a first compression chamber partitioned by contact between an outer curved surface of the spiral wall 10c of the fixed scroll and an inner curved surface of the spiral wall 11c of the orbiting scroll, and a second compression chamber partitioned by contact between an inner curved surface of the spiral wall 10c of the fixed scroll and an outer curved surface of the spiral wall 11c of the orbiting scroll.
In the scroll compressor of this configuration, as illustrated in FIG. 4 which will be described later, the spiral walls are brought into contact with each other by a centrifugal force or the like in association with orbiting of the orbiting scroll 11, and a force originated by the centrifugal force or the like acts on a contact portion between the spiral walls 10c, 11c in a direction orthogonal to a contact surface. Since the spiral wall and the end plate are connected integrally with each other, when the orbiting scroll 11 is at an orbital angle position at which portions other than spiral end portions 102, 112 of the spiral walls (which are terminal ends of wall surfaces which form the compression chamber 15 and are end points of contact points which contribute to compression, that is, positions where closing of the compression chamber 15 starts) come into contact with each other, a contact load acting on the contact portion of the spiral walls is transmitted to and supported by end plates 10a and 11a via connecting portions (connecting portions 10b, 11b) between the spiral walls 10c, 11c and the end plates 10a, 11a extending both sides in the vicinity of the contact portion.
In contrast, when the orbiting scroll 11 is at the orbital angle position at which the spiral end portions 102, 112 of the spiral walls of the scrolls come into contact with the spiral walls of the scrolls of the counterparts, the contact load acting on the contact portion of the spiral walls is transmitted to and supported by the end plate only via the connecting portions with respect to the spiral wall and the end plate extending on one side of the contact portions. Therefore, a shear stress in the vicinity of the contact portion generated at the connecting portion between the spiral walls and the end plates is double the shear stress generated when portions other than the spiral end portions are in contact with each other, so that the spiral walls may be broken unless a sufficient strength is secured on the connecting portions in the vicinities of the spiral end portions.
As the related art relating to an improvement of strength of the spiral end portions of the spiral walls of the scrolls, Patent Literature 1 proposes providing inclined surfaces or stepped surfaces which are gradually reduced in height at spiral end portions of the spiral walls of the scrolls so as to extend therefrom and dispersing stress concentration caused by a centrifugal force. Patent Literature 2 discloses a configuration in which an outer wall and an inner wall of a spiral wall of an orbiting scroll are formed along an involute curve to the spiral end portion, an upper surface of the spiral end portion is set to be relatively lower than other portions to provide a portion which does not contribute to the compression of fluid, and a contact point is provided at this portion so that a pressing force is dispersed owing to the presence of a plurality of the contact points at all the crank angles, whereby likelihood of an occurrence of wear or burning is reduced.